Apparatus for the reversal of color photographic negatives



May 1, 1945.

F. BIEDERMANN APPARATUS FOR THE REVERSAL 0F COLOR PHOTOGRAPHIC NEGATIVES Filed Feb. 1'7, 1942 I E'QIE RICH BmDERmMV filter sets dyed in the Patented May 1, 19 45 PHOTOGRAPHIG NEGATIVES Friedrich Biedermann, Munlch-Unterhacliing,

Germany; vested. in the Alien todian Property Cus- Application February 17, 1942, Serial Nae 1 ,280 I In Germany July9, 19,40

6 Claims. (or. 250 415). I z I My presentinventionrelatesto an apparatus for the reversal of color photographic negatives. This application is a continuation-in-partof my applicationSer. No. 365,455, filed November 13, 1940, Patent 2,295,628, which in turn is a continuation-inmartof my application. 'Ser.. No. 327,047, filed March 30,- 1940, which in turn is a continuation-impart of my application Ser. No. 242,627, matured into Patent 2,214,072, dated Septemberlt), 1940. l l

The known apparatus for the reversal of'blackwhite-negatives consist of an image-converting tube which as an essential part exhibits besides a photoor glowcathodea control electrode provided with a light-sensitive'layer. The electrode controls the emission of electrons starting from the cathode so that a certain amount ofelectrons corresponding to the brightness is removed for each part of the image. Since this amountof electronsdoes 'notfall on the fluorescent screen,

a negative is hence converted into the corresponding positive.

In order to apply such an apparatus for estimating the adaptability for copying a color negative, it is necessary to register the color value of the color negative to be tested by constantly scanning it with the aid of several filters dyed in certain primary colors.

It is an object of my present invention to pro- Vide an improved apparatus for the reversal of color photographic negatives to be estimated by an electric process.

A-further object of my invention is to provide such apparatus comprising two similar filter sets dyed in the primary colors and arranged in such a way that filters of the same color are in the beams of light during the same time interval.

A still further object of the invention is to arrange the, filter sets in the form of rotatable discs driven by a common synchronous motor.

Other objects of my invention will appear from the detailed description following hereinafter.

Reference is made to the accompanying drawing in which Figure 1 represents the view of a reversal apparatus according to the invention,

regard to the observer in such a manner that in scanning the' image filtersjof equal color are simultaneously thepath of rays. Preferably the two' filter sets are constructed as rotatable filterdiscs divided into eventlylarge filter sectors correspondingeto the number of the primary colors. In order to reach-a synchronous movement the filterdiscs aredrivenby a common motor or two motors synchronously kept in any way. Instead of. the rotatable filter discs there may also'be used dyedline screens one of which is arrangedhehmd the negative or in .front of the photo-cathode and the other on the fluo rescent screen. In order to compensatespectral deviations of the light source or of theifiuorescent light. of the screen suitable filters may be placed in the path of rays. Moreover for'removing inaccuracies of color of. the negative theremay be v provided, control filters which are also inserted'into the path of rays of the copying apparatusein CODYiHgthe negative.

In Figure 1, a filter disc Dmounted on a shaft W driven by the motor M is arranged in the path of the rays emitted by the source of light L and penetrating the color negative N between the.

lens 0 and the light source. The photo-cathode is herein shown with a series of spaced electrode elements-Kl, K2, K3, K4 and K5, and a plurality of resistors R. The filter D (Figure 2) of three sectors equal in'size of angle and dyed in three primary colors as, for instance, yellow 9, purple p, and blue-green bar. A second filter D1" is in the path of rays of the observer Y in front of the luminescent screen F and is constructed as a disc filter (Figure 3) having three color sectors g, p, and bgrf (yellow, purple, bluegreen) likewise equal in size of angle in the same manner as the filter D. The filter D1 is mounted Figures 2 and 3 represent views of filter discs used, and

Figure4 represents the View of a reversal apparatus and line screens employed therein.

In accordance with my inventiontwo similar I primary colors are ar ranged in such a way that one filter set is positioned between the color negative and the photo-. cathode and the other in the .path of rays with on the shaft W1 driven bythe motor M1. In order to guarantee a, synchronous rotation of the two filter discs they are driven either by a common motor or as shown in Figure 1 by two motors M and M1 connected with a common network or synchronously kept in any other way. The filters D and D1 are so positioned in the path of rays that'in scanning the image the same filter colors of the both filter discs always are in the In the example path of rays simultaneously. represented in Figures 1-3 the color negative N is illuminated three times during a rotation of the filter discs D, D1, each time in a primary color. For compensating spectral deviations, for instance, of the source of light L or of the fluorescent light of the screen F a suitable compensating filter F2 maybe inserted into the path of consists light. In order to compensate the inaccuracies of color recognized in observing the reversed image of the color negative N, i. e., the color positive on the screenF, control filters St may be inserted into the path of rays, for instance, between the filter disc D and the photo-cathode K. The position of the control filter or filters yields, for instance, the correction of color necessary for the copying of the color negative. The position of the control filter or filters St necessary for the best color reproduction may immediately be used for copying by operatively connecting the mechanism for adjusting the control filter with a corresponding correction filter ofv the color copying apparatus for instance.

Another modification is shown in Figure 4. This apparatus is distinguished from that of Figure 1 by the fact that instead of the filter discs D, D1, there are employed corresponding line screens Lr, Lr1, one of which is placed directly in front of the photo-cathode K or behind the negative N and the other on the fluorescent screen F. The screen lines of the screen Lr correspond to those of the screen Ln and are dyed in primary colors as, for instance, yellow, purple, blue-green. Other combinations as, for instance, red, blue, green may of course also be used. In this apparatus compensating filters Fi for compensating spectral deviations of the light source L and of the fluorescent light of the screen F and control filters St for correcting the color values of the negative may be arranged as already described above as to the apparatus according to Figure 1.

I claim:

1. Apparatus for the reversal of photographic color negatives which comprises an image-converting tube provided with a photo-cathode, a control elctrode having a light-sensitive layer and controlling the electrons emitted by said cathode, and a fluorescent screen, an objective between said cathode and the color negative to be reversed, and two filter sets dyed in identical primary colors, one of said filter sets being arranged in the ray beam path between said negative and said cathode and the other filter set in the ray beam path of the observer in such a manner that identical filter colors always are simultaneously in the ray beam paths in scanning said negative.

2. Apparatus for the reversal of photographic color negatives which comprises an image-converting tube provided with a photo-cathode, a control electrode having a light-sensitive layer and controlling the electrons emitted by said cathode, and a fluorescent screen, an objective between said cathode and the color negative to be reversed, and two filter sets arranged as rotatable discs divided in identical filter sectors corresponding in number to the primary colors, one of said filter sets being arranged in the ray beam path between said negative and said cathode and the other filter set in the ray beam path of the observer in such a manner that identical filter colors always are simultaneously in the ray beam paths in scanning said negative.

3. An apparatus as in claim 1 in which the filter sets are line screens, the screen lines of which are colored with the primary colors.

4. An apparatus as in claim 1 in which at least one control filter is positioned between the negative and the cathode for correcting the color values of the negative.

5. An apparatus as in claim 1 in which at least one compensating filter is positioned in the ray beam path from the fluorescent screen to compensate for spectral deviations.

6. An apparatus as in claim 2 in which at least one control filter is positioned between the negative and the cathode for correcting the color values of the negative and at least one compensating filter in the ray beam path from the fluorescent screen to compensate for spectral deviations.

FRIEDRICH BIEDERMANN. 

